Will I gain after going back to maintenance?

Okay so I’m sorry if this is a silly question but I’m kind of worried 🙈 I was wondering if by going up to maintenance I’d end up gaining weight after being in a deficit for quite a while? I’ve been in a deficit & eating between 1300-1500 for quite a few months which I’m not particularly bothered about but the issue is that I run like a lot so almost every day and my mileage is quite high weekly and I go to the gym a couple days a week so I’m assuming that I burn off quite a lot & I’m dropping weight quite a lot which is getting a little too much (for reference I’m like 5’6 & 50kg ish). So if I just suddenly go up to maintenance will I gain a ton of weight back or something, and how do I even work out my maintenance without majorly overestimating since I’m literally terrified of gaining weight loll. Sorry if this is a silly question and any advice is appreciated thank you!!